This invention relates generally to combustion devices and, more particularly, to emission control systems for combustion devices.
During a typical combustion process within a furnace or boiler, for example, a flow of combustion exhaust gas is produced. The combustion exhaust gas typically contains combustion products including, without limitation, carbon dioxide, carbon monoxide, water, hydrogen, nitrogen and mercury generated as a direct result of combusting solid and/or liquid fuels. Before the combustion exhaust gas is emitted into the atmosphere, combustion products, such as mercury (Hg) emissions and oxides of nitrogen (NOx), are typically removed according to regulatory and/or other environmental standards and procedures that include, but are not limited to, United States (U.S.) and State-specific Environmental Protection Agencies' (EPA) requirements, local ordinances, industry standards and corporate policies.
Many known combustion exhaust gas streams include Hg in the elemental form of Hg0 at elevated temperatures typically in excess of 538 degrees Celsius (° C.) (1000 degrees Fahrenheit (° F.)). One known method of Hg0 removal includes oxidation of at least a portion of the Hg0 at temperatures below 538° C. (1000° F.) using a chlorine-(Cl) containing species or other oxidizing agents, thereby forming at least some Hg+2. Such oxidizing reactions typically form at least some HgCl2. Generally, Hg+2 is more reactive than Hg0 and, therefore, Hg+2 is more easily removed from the combustion exhaust gas stream than Hg0. The efficiency and effectiveness of Hg removal from a combustion exhaust gas stream depend on the methods and apparatus for facilitating the formation, concentration and distribution of Hg+2 within the combustion exhaust gas stream as well as the integration of such Hg removal methods and apparatus to existing combustion exhaust gas methods and apparatus.